The present invention generally relates to seat belt retractors which include a means for absorbing or dissipating crash energy. More particularly, the present invention relates to a seat belt retractor having a multi-level reaction force generating torsion bar therein.
In a conventional seat belt retractor, a web or a vehicle (often called inertial) sensor is used to stop the rotation of a spool to prevent the protraction of the seat belt webbing during an accident. A second class of seat belt retractors permits the controlled protraction of the seat belt by incorporating within the retractor an energy absorption (or dissipation) mechanism which permits the spool to rotate after the retractor has been initially locked up. In the past these mechanisms have included crushable bushings (U.S. Pat. No. 5,547,143), deformable tubes (U.S. Pat. No. 3,881,667) or torsion bars (U.S. Pat. No. 3,741,494).
It is an object of the present invention to provide an energy absorbing retractor that has one or more load limiting levels, a retractor that may be activated either mechanically, electrically or pyrotechnically, and one which utilizes a unique energy absorbing (dissipating) mechanism.
Accordingly the invention comprises: an energy absorbing retractor having a frame, locking mechanisms to initially stop a spool from rotating in a belt protraction direction, the spool being rotationally supported relative to the frame, a seat belt wound about the spool, bias means to retract the seat belt, and torsion bar means for generating at least a first level of reaction torque on the spool permitting the spool to rotate in a controlled manner in a belt protracting direction including a torsion bar having a middle portion and a first torsion rod (or torque or torsion tube) extending therefrom, the middle portion fixedly coupled to the spool to prevent relative rotation therebetween, the first torsion rod including a first end coupled to first locking mechanisms to prevent the first end from rotating upon such coupling, whereby upon locking of the first end, and the loading of the spool, the first torsion rod is twisted, permitting the spool to rotate, to generate a first level of control force. A second torsion rod (or torque or torsion tube) is provided which can generate a second level of reaction force. A third level of reaction force is attainable if both torsion rods are activated relatively simultaneously.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.